Short-circuit protection device for a DC control element

• US 4,439,806 A
• Filed: 03/05/1982
• Issued: 03/27/1984
• Est. Priority Date: 03/12/1981
• Status: Expired due to Fees

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Brajder, Antonio
• Primary Examiner(s): Salce, Patrick R.
• Application Number:
  US06/354,929
• Time in Patent Office: 753 Days
• Field of Search: 361/98, 361/93, 361/94, 361/100, 361/31, 361/23, 361/30, 361/95, 361/96, 363/55, 363/56, 363/50, 363/58, 363/52, 363/53, 363/132, 330/207 P, 330/298
• US Class Current: 361/98
• CPC Class Codes: H02H 7/0838 with H-bridge circuit

Abstract

A short-circuit protection device for a DC control element has at least one transistor which is addressed by timing pulses obtained by comparison of a triangular voltage with a control voltage. Each such transistor is provided with a separate overcurrent protection device which, after a short circuit, blocks the associated transistor until the beginning of a new switching-on pulse. The control voltage assumes values which are above the maximum value of the triangular voltage.

In the event of a short circuit, the transistor concerned is switched off very fast, but is switched on again by the next succeeding switching-on pulse and a determination is made as to whether the short circuit is still present. If the control voltage rises to values which are above the maximum value of the triangular voltage because the actual value of the load current deviates heavily from the reference value due to the disconnection of the transistors, the transistors remain switched off until the DC control element is restored to operation by external intervention.

Claims

1. A circuit for protecting a DC control element from short-circuits, the DC control element including at least one transistor having an input for timing pulses, comprising:

a. a controlllor having as inputs a desired current and the actual load current of the DC control element and providing an output which is a control voltage proportional to the difference therebetween;

b. a comparison stage having as inputs a triangular voltage having a predetermined maximum value and said control voltage, said control voltage being permitted to assume values greater than said predetermined maximum value, said comparison stage providing timing outputs existing for a duration corresponding to the duration over which said triangular voltage exceeds said control voltage, said timing pulses being provided to the inputs of each transistor in said DC control element; and

c. an overload protection device for each transistor, each overload protection device coupled to the respective transistor and having timing pulses from said comparison stage as an input, each overload protection device responsive to an overcurrent in the transistor to block the transistor and keep it blocked until the start of a new timing pulse, whereby in the case of an overload, said control voltage will exceed said maximum value of said triangular voltage thereby assuring that no pulses are generated until the overload condition is removed thereby avoiding repeated switching on and off of said overload protection devices.

2. A circuit in accordance with claim 1 and further comprising:

a second comparison stage having the actual value of the load current and a reference value as inputs and providing an output signal when the difference between the actual value and the reference value exceed a predetermined limit; and

a trouble alarm device having the output signal of the second comparison stage as an input.

3. A circuit in accordance with claim 2 and further comprising:

a delay stage having the output of the second comparison stage as an input and having a delayed output signal; and

a disconnecting device coupled to the input of the DC control circuit and having the output signal of the delay stage as an input.