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An automated external defibrillator analyzes the heart’s electrical activity and determines whether a defibrillation shock is needed. Within its power circuit, a capacitor stores the electrical energy that the output stage releases as a controlled pulse through the electrode pads.
For equipment designers, this makes capacitor selection an important part of both electrical and mechanical development. Stored energy, discharge conditions, charge retention, and available enclosure space all influence the choice.
The CRE DEMJ-PC aluminum-case pulse film capacitor featured here is rated at 2,000 V DC, 100 μF ±5%. Its cylindrical aluminum housing, sealed top, and insulated leads provide a configuration for evaluation in AED energy storage assemblies.
CRE DEMJ-PC 2,000 V DC 100 μF aluminum-case pulse film capacitor
The charging circuit transfers energy from the battery into the storage capacitor. When a shock is required, the output switching circuit controls the discharge through the electrodes. The capacitor supplies stored energy; the device’s sensing and control systems determine whether and how a shock is delivered.
（Inside an AED, highlighting the battery and energy-storage capacitors. Adapted from How It Works, Issue 116. How It Works）
Capacitance and charging voltage establish the energy available before discharge. The waveform, circuit impedance, and switching sequence then determine the demands placed on the capacitor during the pulse. Evaluating these factors together connects component selection to the intended AED operating profile.
The featured aluminum-case configuration has the following specifications and construction details.
Parameter | Featured DEMJ-PC configuration |
Rated voltage | 2,000 V DC |
Nominal capacitance | 100 μF |
Capacitance tolerance | ±5% |
Housing | Cylindrical aluminum case |
Connections | Insulated red and white wire leads |
Construction marking | Dry, PUR |
Self-healing marking | SH |
Temperature marking | −40°C to +85°C |
At a charging voltage of 2,000 V, the 100 μF capacitor stores a nominal 200 J of energy. This is the energy stored in the capacitor, rather than a specification for energy delivered to the patient. Delivered energy depends on the discharge circuit, residual energy, waveform, and load conditions.
In metallized film capacitors, self-healing can isolate a localized dielectric breakdown, allowing the remaining active area to continue functioning.
For pulse applications, this characteristic is considered alongside capacitance stability and endurance under the intended electrical stress. It does not replace evaluation of repeated charging and discharging in the actual circuit.
An AED energy storage capacitor experiences distinct charging, holding, and discharge conditions. Selection therefore extends beyond voltage and capacitance to include charging duration, voltage hold time, peak current, pulse repetition, and temperature.
CRE’s DEMJ-PC technical specifications cover charging and discharging conditions, self-discharge characteristics, and pulse endurance under defined loads and temperatures. This information helps engineers assess capacitor suitability for their application.
Charge retention is important during the interval between charging and discharging. Pulse endurance also requires careful evaluation, as cycle count alone does not reflect the effects of load and operating temperature.
The DEMJ-PC features two insulated leads extending from the sealed top of its cylindrical aluminum housing. This arrangement allows lead routing and connection placement to be considered alongside the charging board, switching stage, and mounting structure.
Mechanical integration includes securing the capacitor, protecting the leads from strain, and providing suitable insulation and clearance around the conductive housing.
Customizing Capacitors with CRE
CRE’s DEMJ-PC documentation includes custom dimensions and configurations with different lead lengths and terminal arrangements. For an aluminum-case project, these options provide a starting point for discussing the enclosure space and electrical interface.
Share the target charging voltage, required stored energy, discharge profile, operating temperature, and mechanical constraints with CRE. This information helps evaluate suitable capacitor configurations.
Explore CRE capacitor solutions or contact the engineering team to discuss DEMJ-PC integration into your AED platform.
1. What is the role of the DEMJ-PC capacitor in an AED?
The product label specifies a rated voltage of 2,000 V DC, a capacitance of 100 μF ±5%, and a temperature range of −40°C to +85°C. It also carries SH, dry (PUR), and IEC 61071 markings. The capacitor features a cylindrical aluminum housing with insulated red and white leads.
2. Does 200 J of stored energy mean the AED delivers 200 J to the patient?
No. At a charging voltage of 2,000 V, the 100 μF capacitor stores a nominal 200 J of energy. The energy delivered through the electrodes depends on the discharge waveform, circuit losses, residual capacitor energy, and load conditions.
3. What information is needed to select a DEMJ-PC capacitor for an AED?
Provide the required capacitance, charging voltage, target stored energy, peak discharge current, pulse duration, and repetition rate. Voltage hold time, operating temperature, available space, mounting requirements, and connection details also help CRE assess the configuration.
4. Can CRE customize the capacitor dimensions and connections?
Yes. CRE can review dimensional and connection requirements for a customized DEMJ-PC solution. Share the available enclosure space, preferred lead lengths, terminal arrangement, and electrical operating conditions. Options for the aluminum-case version should be agreed during the technical review.
5. Can CRE evaluate DEMJ-PC as a replacement for an existing capacitor?
Yes. CRE can assess an existing part number, datasheet, drawing, or specification to evaluate a potential replacement. The review should cover electrical performance, pulse conditions, insulation, dimensions, and connections. Suitability must then be verified in the intended AED circuit.
