DC-DC converter for boosting input voltage at variable frequency

• US 20050206361A1
• Filed: 03/10/2005
• Published: 09/22/2005
• Est. Priority Date: 03/17/2004
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Ito, Masahiko
• Granted Patent: US 7,285,939 B2
• Time in Patent Office: Days
• US Class Current: 323/282
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

A DC-DC converter for boosting an input voltage to a higher output voltage includes an inductor, a field effect transistor, a first ON signal generating circuit, a second ON signal generating circuit, an OFF signal generating circuit, a transistor driving signal generating circuit, and a switching frequency varying circuit. The switching frequency varying circuit changes a first ON time with the passage of time, so that the energy of switching noise is diffused without concentrating at specific frequencies. Thus, magnitude of the energy of switching noise in each switching frequency can be reduced.

Claims

1. A DC-DC converter for an electric load comprising:

a DC power supply;

a coil connected to the DC power supply;

a switching element that is connected to the coil and controls a coil current supplied to the coil from the DC power supply by performing switching operations to produce a boosted output voltage for the electric load;

a switching element driving signal generating circuit that generates a switching element driving signal for switching the switching element based on the coil current and the output voltage; and

a switching frequency varying circuit that changes a switching frequency of the switching element driving signal with passage of time regardless of the output voltage.

2. The DC-DC converter according to claim 1 further comprising:

a first ON signal generating circuit that determines a first ON time of the switching element based on a result of comparison between the coil current and a specified current threshold value, while generating a first ON signal corresponding to the first ON time;

a second ON signal generating circuit that determines a second ON time of the switching element based on a result of comparison between the output voltage and a specified voltage threshold value, while generating a second ON signal corresponding to the second ON time; and

an OFF signal generating circuit that generates an OFF signal corresponding to a specified OFF time of the switching element,

wherein the switching element driving signal generating circuit generates the switching element driving signal based on the first ON signal, the second ON signal and the OFF signal.

3. The DC-DC converter according to claim 2,

wherein the switching frequency varying circuit changes the first ON time with the passage of time.

4. The DC-DC converter according to claim 3,

wherein the switching frequency varying circuit changes the specified current threshold value with the passage of time.

5. The DC-DC converter according to claim 1,

wherein the switching frequency varying circuit includes a triangular voltage generating circuit that generates a triangular voltage.

6. The DC-DC converter according to claim 5,

wherein the switching frequency varying circuit includes a counter circuit that counts the number of switching operations of the switching element, and a reference power circuit that successively switches and outputs plural voltages of different magnitudes based on a result of counting by the counter circuit.

7. The DC-DC converter according to claim 2,

wherein the switching frequency varying circuit changes the specified OFF time.

8. The DC-DC converter according to claim 7,

wherein the OFF signal generating circuit generates an OFF signal corresponding to the specified OFF time based on a result of comparison between a voltage of a capacitor charged with a specified charging current and a specified OFF time threshold value, and

the switching frequency varying circuit changes the specified charging current with the passage of time.

9. The DC-DC converter according to claim 8,

wherein the switching frequency varying circuit includes a triangular voltage generating circuit that generates a triangular voltage, and a voltage-current conversion circuit that converts the triangular voltage into a current corresponding to the triangular voltage.

10. The DC-DC converter according to claim 7,

wherein the OFF signal generating circuit generates a plurality of OFF signals corresponding to specified different OFF times, and

wherein the switching frequency varying circuit includes a counter circuit that counts the number of switching operations of the switching element, and an OFF signal switching circuit that successively switches and outputs the plurality of OFF signals based on a result of counting by the counter.

11. The DC-DC converter according to claim 2,

wherein the switching element, the first ON signal generating circuit, the second ON signal generating circuit, the OFF signal generating circuit, the switching element driving signal generating circuit and the switching frequency varying circuit are integrally formed as an integrated circuit.

12. The DC-DC converter according to claim 1,

wherein the load includes a vehicle passenger protecting device for protecting vehicle passengers.