Compact low noise low power dual mode battery charging circuit
First Claim
1. A battery charger comprising in combination:
- (a) a first rectifier receiving a line voltage and producing a rectified sinusoidal voltage;
(b) a transformer having a primary winding coupled to receive the rectified sinusoidal voltage and first and second secondary windings, a second rectifier being coupled between terminals of the first secondary winding and terminals of a battery;
(c) a switch coupled between a terminal of the primary winding and means for producing a signal indicative of current flowing through the switch and primary winding;
(d) first means coupled to terminals of the second secondary winding for producing a battery condition voltage representative of a voltage between the terminals of the battery;
(e) peak detect and hold means coupled to receive a voltage proportional to the battery condition voltage and detect and hold a peak value thereof;
(f) second means for comparing an output voltage of the peak detect and hold means with the voltage proportional to the battery condition voltage to produce a charging mode signal when the voltage proportional to the battery condition voltage falls a predetermined threshold voltage below the output voltage of the peak detect and hold means; and
(g) third means coupled to receive the charging mode signal and the signal indicative of current flowing through the primary winding for producing a control signal applied to the switch to control flow of current through the primary winding in accordance with the battery condition voltage, the third means including means for producing a constant turn off time for the switch and means for varying turn on time for the switch in response to the signal indicative of current flowing through the primary winding.
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Accused Products
Abstract
A low noise battery charger includes a rectifier to convert AC line voltage to a rectified sinusoidal voltage that is applied to a primary winding of a transformer. Another rectifier coupled to a first secondary winding applies a charging current to a battery. A switch coupled in series with the primary winding controls current therein. A rectifier coupled to another secondary winding produces a battery condition voltage. An incrementing signal synchronized with the rectified sinusoidal voltage increments a ratchet DAC until its output voltage exceeds the battery condition voltage. A low charging mode signal is produced when the battery condition voltage falls a certain amount below the DAC output voltage. Flow of current through the primary winding is controlled by operating the switch at a relatively high frequency and by producing constant turn off times for the switch and also by modulating turn on times for the switch in response to the signal indicative of primary winding current. Maximum power transfer across the transformer is thereby achieved without flyback voltage of the transformer exceeding breakdown voltage of the switch, and zero current switching is achieved.
29 Citations
22 Claims
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1. A battery charger comprising in combination:
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(a) a first rectifier receiving a line voltage and producing a rectified sinusoidal voltage; (b) a transformer having a primary winding coupled to receive the rectified sinusoidal voltage and first and second secondary windings, a second rectifier being coupled between terminals of the first secondary winding and terminals of a battery; (c) a switch coupled between a terminal of the primary winding and means for producing a signal indicative of current flowing through the switch and primary winding; (d) first means coupled to terminals of the second secondary winding for producing a battery condition voltage representative of a voltage between the terminals of the battery; (e) peak detect and hold means coupled to receive a voltage proportional to the battery condition voltage and detect and hold a peak value thereof; (f) second means for comparing an output voltage of the peak detect and hold means with the voltage proportional to the battery condition voltage to produce a charging mode signal when the voltage proportional to the battery condition voltage falls a predetermined threshold voltage below the output voltage of the peak detect and hold means; and (g) third means coupled to receive the charging mode signal and the signal indicative of current flowing through the primary winding for producing a control signal applied to the switch to control flow of current through the primary winding in accordance with the battery condition voltage, the third means including means for producing a constant turn off time for the switch and means for varying turn on time for the switch in response to the signal indicative of current flowing through the primary winding. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A battery charger comprising in combination:
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(a) a first rectifier receiving a line voltage and producing a rectified sinusoidal voltage; (b) a transformer having a primary winding coupled to receive the rectified sinusoidal voltage and first and second secondary windings, a second rectifier being coupled between terminals of the first secondary winding and terminals of a battery; (c) a switch coupled between a terminal of the primary winding and means for producing a signal indicative of current flowing through the primary winding; (d) first means coupled to terminals of the second secondary winding for producing a battery condition voltage representative of a voltage between the terminals of the battery; (e) second means responsive to the rectified sinusoidal voltage for producing a timing signal; (f) a ratchet DAC; (g) third means coupled to an output of the ratchet DAC for comparing an output voltage of the ratchet DAC to a voltage proportional to the battery condition voltage and producing an incrementing signal synchronized with the timing signal to increment the ratchet DAC until the ratchet DAC output voltage exceeds the voltage proportional to the battery condition voltage; (h) fourth means coupled to the output of the ratchet DAC for producing a low charging mode signal when the reference voltage falls a predetermined threshold voltage below the DAC output voltage; (i) fifth means coupled to receive the low charging mode signal and the signal indicative of current flowing through the primary winding for producing a control signal applied to the switch to control flow of current through the primary winding in accordance with the battery condition voltage.
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15. A method of charging a battery using a battery charger, comprising the steps of:
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(a) rectifying an AC line voltage to produce a sinusoidal rectified voltage and applying it to a primary winding of a transformer, the transformer having first and second secondary windings, a rectifier being coupled between terminals of the first secondary winding and terminals of a battery to supply a rectified charging current to the battery; (b) operating a switch coupled between a terminal of the primary winding to control current through the primary winding; (c) producing a signal indicative of primary winding current; (d) producing a battery condition voltage between terminals of the second secondary winding, the battery condition voltage being representative of voltage between the terminals of the battery; (e) detecting and storing a peak value of a reference voltage proportional to the battery condition voltage; (f) comparing the stored peak value with the voltage proportional to the battery condition voltage to produce a charging mode signal with a low charging mode state when the voltage falls a predetermined threshold voltage below the peak value; and (g) controlling flow of current through the switch by turning the switch off for constant times and turning the switch on for times which vary in response to the signal indicative of the primary winding current. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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22. A battery charger comprising in combination:
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(a) a first rectifier receiving a line voltage and producing a rectified sinusoidal voltage; (b) a transformer having a primary winding coupled to receive the rectified sinusoidal voltage and first and second secondary windings, a second rectifier being coupled between terminals of the first secondary winding and terminals of a battery; (c) a switch coupled between a terminal of the primary winding and means for producing a signal indicative of current flowing through the switch and primary winding; (d) first means coupled to terminals of the second secondary winding for producing a battery condition voltage representative of a voltage between the terminals of the battery; (e) peak detect and hold means coupled to receive a voltage proportional to the battery condition voltage and detect and hold a peak value thereof; (f) second means for comparing an output voltage of the peak detect and hold means with the reference voltage to produce a charging mode signal when the voltage proportional to the battery condition voltage falls a predetermined threshold voltage below the output voltage of the peak detect and hold means; and (g) third means coupled to receive the charging mode signal and the signal indicative of current flowing through the primary winding for producing a control signal applied to the switch to control flow of current through the primary winding in accordance with the battery condition voltage.
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Specification