Design Note 27 Issue 1 February 1996 Design Note 27 Issue1 February 1996 +12V 12V Solenoid Driver/Latch Single Switch Operated, High Current High Side Switch 270 ZTX550 ZTX550 This circuit has been designed to control a solenoid by the operation of a single push-button switch. It will supply loads of over 1A and can be operated up to a maximum speed of once every 0.6 seconds. When power is first applied to the circuit, the solenoid will always start in it's off position. Other features of the circuit are it's automatic turn-off if the load is shorted, and virtually zero power consumption when off. When the supply is connected, the 470 and 270 base-emitter resistors ensure all three transistors remain off. The 1F capacitor charges up to a value approaching that of the supply rail. If the push-button switch is then closed, the charge is transferred to the bias network of the ZTX300, turning it on. This, through the 100 a n d 2 7 0 b i a s resistors of the ZTX550s turn these devices on which energises the load. This action also holds the ZTX300 on (via the two 560 resistors), irrespective of the decaying charge on C1. 100 2W dissipated in the 1N4000 protection diode. When the push-button switch is released, the 1F capacitor will charge up ready to trigger the latch on again when the switch is operated. The 0.1F capacitor inhibits false triggering due to transient voltages. This circuit was originally designed for an Automotive application, but similar circuits should also find use in industrial control systems. Similar circuits for higher current applications are possible with a change to the output device. For example, the ZTX751 2A rated PNP, or the high gain ZTX790A could be used for load currents of up to 2A, while the ZTX951 allows operation to over 3A. 560 560 27K ZTX300 1F 0.1 470 Figure 1 12V Latch Circuit. Since the ZTX300 is now on, when the p u s h - b u t t o n i s r e l e a s e d t h e 1F capacitor will be discharged through the transistor via the bleed resistor. If the push-button is operated again it will connect this discharged capacitor to the bias network of the ZTX300 turning it and thus the output off. Any excess energy stored in the solenoid will be DN27 - 1 DN 27 - 2 1N4000 1A SOLENOID Design Note 27 Issue 1 February 1996 Design Note 27 Issue1 February 1996 +12V 12V Solenoid Driver/Latch Single Switch Operated, High Current High Side Switch 270 ZTX550 ZTX550 This circuit has been designed to control a solenoid by the operation of a single push-button switch. It will supply loads of over 1A and can be operated up to a maximum speed of once every 0.6 seconds. When power is first applied to the circuit, the solenoid will always start in it's off position. Other features of the circuit are it's automatic turn-off if the load is shorted, and virtually zero power consumption when off. When the supply is connected, the 470 and 270 base-emitter resistors ensure all three transistors remain off. The 1F capacitor charges up to a value approaching that of the supply rail. If the push-button switch is then closed, the charge is transferred to the bias network of the ZTX300, turning it on. This, through the 100 a n d 2 7 0 b i a s resistors of the ZTX550s turn these devices on which energises the load. This action also holds the ZTX300 on (via the two 560 resistors), irrespective of the decaying charge on C1. 100 2W dissipated in the 1N4000 protection diode. When the push-button switch is released, the 1F capacitor will charge up ready to trigger the latch on again when the switch is operated. The 0.1F capacitor inhibits false triggering due to transient voltages. This circuit was originally designed for an Automotive application, but similar circuits should also find use in industrial control systems. Similar circuits for higher current applications are possible with a change to the output device. For example, the ZTX751 2A rated PNP, or the high gain ZTX790A could be used for load currents of up to 2A, while the ZTX951 allows operation to over 3A. 560 560 27K ZTX300 1F 0.1 470 Figure 1 12V Latch Circuit. Since the ZTX300 is now on, when the p u s h - b u t t o n i s r e l e a s e d t h e 1F capacitor will be discharged through the transistor via the bleed resistor. If the push-button is operated again it will connect this discharged capacitor to the bias network of the ZTX300 turning it and thus the output off. Any excess energy stored in the solenoid will be DN27 - 1 DN 27 - 2 1N4000 1A SOLENOID