Voltage clamp circuit for switched inductive loads

• US 4,658,203 A
• Filed: 03/07/1986
• Issued: 04/14/1987
• Est. Priority Date: 12/04/1984
• Status: Expired due to Fees

• Current Assignee: Airborne Electronics Incorporated
• Original Assignee: Airborne Electronics Incorporated
• Inventors: Freymuth, William P.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Ault, Anita M.
• Application Number:
  US06/838,425
• Time in Patent Office: 403 Days
• Field of Search: 323/282, 323/284, 323/286, 323/287, 361/33, 361/91, 361/100, 361/111, 357/23.13
• US Class Current: 323/282
• CPC Class Codes: H03K 17/0822 in field-effect transistor switches
• CPC Class Codes: H03K 17/687 the devices being field-effect transistors

Abstract

When in control circuit for varying the current through an inductive load the current is sent as pulses of variable width and each time that occurs is cut off by the electronic switch in series with the load across the power line a high inductive voltage is generated. When the electronic switch control terminal is disabled, the electronic switch will turn off and no current can flow through the switch. Thus, the inductive energy in the load, since it cannot continue to flow, generates a very high inductive voltage which can do damage to equipment and personnel. A clamping circuit is provided by means of two series diodes. One diode is a Zener diode with known breakdown potential. The other is a simple diode. The Zener diode has its cathode tied to the junction between the switch and the load and the simple diode has its cathode attached to the control electrode of the electronic switch. When the switch is opened and the inductive voltage appears at the junction between the load and the switch, the voltage tends to flow through the Zener diode and the simple diode. When this current flows through the Zener diode and the simple diode to the control electrode of the electronic switch, the electronic switch will turn on and will momentarily carry to ground the current that wants to flow from the load through the switch to ground. As this current drops to zero, the inductive voltage drops to zero, the electronic switch turns off and the system is disabled until the next control pulse is received on the electronic switch.

Claims

1. In a control system in which a current is passed through an inductive load by controlling an electronic switch means in series with said inductive load across a power supply by opening and closing said switch with a control voltage on a control voltage lead;

the improvement comprising means to clamp the inductive voltage generated by said inductive load as said current flowing through said load is cut off by the opening of said electronic switch means with said control voltage, said clamp means further comprising;

(a) circuit means having a first terminal connected to the junction of said load and switch; and

a second terminal connected to said control voltage lead; and

(b) said circuit means having a Zener diode and a simple diode connected in series with either their cathodes together, or their anodes together, and the cathode of said simple diode connected toward said control voltage lead, and the cathode of said Zener diode connected toward said first terminal;

whereby when the control voltage is removed from said electronic switch means, said electronic switch means opens, and an inductive voltage peak appears on said first terminal;

current flows in reverse through said Zener diode and through said simple diode thereby generating a control voltage to turn on said electronic switch means passing current through said switch until the inductive voltage is dissipated;

removing said generated voltage from said control lead and opening said electronic switch means until the next load carrying cycle begins.

2. The apparatus as in claim 1 in which the electronic switch means comprises at least one Power MOSFET as said switch means.