MIC5016/5017

Micrel

October 1998

7

MIC5016/5017

1/2 MIC5016

OFF

ON

IRFZ40

24V

Gate

Gnd

Source

Input

V+

5k

Ω

1N4005

ASCO

8320A

Solenoid

Typical Applications

Variable Supply Low Side Driver for Motor Speed Control

(Figure 6) The internal regulation in the MIC5016/17 allows

a steady gate enhancement to be supplied while the MIC5016/

17 supply varies from 5V to 30V, without damaging the

internal gate to source zener clamp. This allows the speed of

the DC motor shown to be varied by varying the supply

voltage.

Figure 6: DC Motor Speed Control/Driver

Solenoid Valve Driver (Figure 7) High power solenoid valves

are used in many industrial applications requiring the timed

dispensing of chemicals or gases. When the solenoid is

activated, the valve opens (or closes), releasing (or stopping)

fluid flow. A solenoid valve, like all inductive loads, has a

considerable “kickback” voltage when turned off, as current

cannot change instantaneously through an inductor. In most

applications, it is acceptable to allow this voltage to momen-

tarily turn the MOSFET back on as a way of dissipating the

inductor's current. However, if this occurs when driving a

solenoid valve with a fast switching speed, chemicals or

gases may inadvertantly be dispensed at the wrong time with

possibly disasterous consequences. Also, too large of a

kickback voltage (as is found in larger solenoids) can damage

the MIC5016 or the power FET by forcing the Source node

below ground (the MIC5016 can be driven up to 20V below

ground

before this happens).

A catch diode has been

included in this design to provide an alternate route for the

inductive kickback current to flow. The 5k

Ω resistor in series

with this diode has been included to set the recovery time of

the solenoid valve.

Figure 7: Solenoid Valve Driver

Figure 5. High Side Driver with Delayed Overcurrent Shutdown

1/2 MIC5017

Gate

Gnd

Source

Input

V+

10µF

R4

1k

Ω

R

S

0.06

Ω

12V

On

R1

1k

Ω

R2

120k

Ω

LM301A

2.2k

Ω

0.01µF

LM3905N

1

2

3

4

8

7

6

5

Logic

V+

Gnd

R/C

V

REF

Trigger

Emit

Coll

12V

1000pF

1k

Ω

1/2 MIC5017

OFF

ON

IRF540

Gate

Gnd

Source

Input

V+

M