Browse Prior Art Database

Closed Loop Solenoid Driver

IP.com Disclosure Number: IPCOM000051018D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Bolash, JP: AUTHOR

Abstract

A magnet driver having negative feedback loop to limit magnet current is disclosed. A second feedback loop is provided to compensate for instability introduced by the collector to base capacitance and DC forward gain roll-off of the driving power transistor. Using a second feedback loop permits advantage to be taken of the amplification of the feedback amplifier to reduce the amount of negative feedback capacitance required.

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Closed Loop Solenoid Driver

A magnet driver having negative feedback loop to limit magnet current is disclosed. A second feedback loop is provided to compensate for instability introduced by the collector to base capacitance and DC forward gain roll-off of the driving power transistor. Using a second feedback loop permits advantage to be taken of the amplification of the feedback amplifier to reduce the amount of negative feedback capacitance required.

Fig.1 shows a power transistor 11 connected in series with a magnet 13 and a current-sensing resistor 15. Spike-suppressing diode 17 and resistors 19 and 21 protect transistor 11 from inductive voltage surges. Transistor 11 receives base current from resistor 23. When the input signal is positive, input transistor 25 conducts base current away from transistor 11 turning transistor 11 off. When the input signal is at or near zero volts, transistor 25 does not conduct, permitting base current to flow to transistor 11, applying approximately +V across magnet
13. As the magnet current rises, the voltage across resistor 15 increases. When the voltage across resistor 15 equals the reference voltage VR, summing amplifier 27 and transistor 29 turn on linearly in negative feedback mode to maintain the voltage across resistor 15 equal to the reference voltage VR. This limits the magnet current to VR/R15 amps. Capacitor 33 and resistor 35 provide a second loop B with compensating AC feedback. When the input signal line returns positive, transistor 11 turns off and the magnet current goes to zero through diode 17 and resis...